There are many factors that contribute to speciation events.
Importantly in plants, pollinators can have a large impact on breeding
between different individuals. This discrimination of pollinators is
driven by a variety of morphological traits in the plant, therefore
possibly leading specific pollinators to having a strong plant
preference. This knowledge leads to the question: Do pollinators
discriminate between subspecies of rabbitbrush? Studying these
differences can be important for predicting gene flow and how speciation
events may start to occur.
Here is some background information
about the study organism to better understand the data presented below.
Rabbitbrush (Ericameria nauseosa) is a native
perennial shrub in the Asteraceae family. Rabbitbrush has erect stems
and commonly has numerous leaves. When flowers bloom in late summer and
fall they are bright yellow and are in clusters. Around 21 species of
rabbitbrush have been described within North America and placed in gray
or green colored groups (genotypes), both of which can be deciduous or
non-deciduous. Within these subspecies ranges are variable with some
being very narrowly isolated but many being widely distributed with
overlapping ranges (McArthur et al., 1986). Within these overlapping
subspecies they are often found growing together. Despite these
morphological and ecological differences little if any work has been
done on the ability of pollinators to discriminate between subspecies,
resulting in a significant gap in our knowledge of how these subspecies
are maintained.
To start researching this question 5 sites were chosen across
Salt Lake and Utah Counties (see the interactive map below). At each
site the green and gray genotypes were identified.
Cuttings of each genotype where collected and pressed. Later in
the lab, the corolla length, width and anther length were determined and
created into the data set below.
| site | color | decid | corolla_length | corolla_width | anther_length |
|---|---|---|---|---|---|
| Midvale | Gray | FALSE | 5.00 | 1.00 | 2.50 |
| Midvale | Gray | FALSE | 5.00 | 1.25 | 3.00 |
| Midvale | Gray | FALSE | 5.00 | 1.00 | 3.00 |
| Midvale | Gray | FALSE | 5.50 | 1.00 | 2.00 |
| Midvale | Gray | FALSE | 5.50 | 1.00 | 2.00 |
| Midvale | Green | FALSE | 4.00 | 1.25 | 3.50 |
| Midvale | Green | FALSE | 4.25 | 1.00 | 2.25 |
| Midvale | Green | FALSE | 4.00 | 1.00 | 3.00 |
| Midvale | Green | FALSE | 4.50 | 1.25 | 3.00 |
| Midvale | Green | FALSE | 4.50 | 1.00 | 3.00 |
| Inlet_Park | Gray | FALSE | 5.00 | 1.00 | 5.50 |
| Inlet_Park | Gray | FALSE | 5.00 | 1.00 | 2.50 |
| Inlet_Park | Gray | FALSE | 5.00 | 1.00 | 4.00 |
| Inlet_Park | Gray | FALSE | 5.00 | 1.00 | 3.50 |
| Inlet_Park | Gray | FALSE | 4.00 | 1.00 | 3.00 |
| Inlet_Park | Green | TRUE | 4.00 | 0.75 | 1.50 |
| Inlet_Park | Green | TRUE | 3.50 | 1.00 | 1.50 |
| Inlet_Park | Green | TRUE | 4.00 | 1.00 | 1.50 |
| Inlet_Park | Green | TRUE | 3.50 | 0.75 | 1.50 |
| Inlet_Park | Green | TRUE | 3.00 | 1.00 | 4.00 |
| Bluffdale | Gray | FALSE | 5.00 | 1.00 | 3.50 |
| Bluffdale | Gray | FALSE | 5.00 | 1.00 | 3.00 |
| Bluffdale | Gray | FALSE | 5.00 | 1.00 | 4.00 |
| Bluffdale | Gray | FALSE | 4.50 | 1.00 | 3.00 |
| Bluffdale | Gray | FALSE | 4.00 | 1.00 | 3.50 |
| Bluffdale | Gray | FALSE | 8.00 | 1.25 | 3.00 |
| Bluffdale | Gray | FALSE | 6.50 | 1.25 | 3.00 |
| Bluffdale | Gray | FALSE | 7.00 | 1.00 | 2.50 |
| Bluffdale | Gray | FALSE | 7.00 | 1.00 | 3.00 |
| Bluffdale | Gray | FALSE | 7.50 | 1.25 | 3.25 |
| Bluffdale | Green | FALSE | 4.00 | 1.00 | 3.00 |
| Bluffdale | Green | FALSE | 4.50 | 1.00 | 3.00 |
| Bluffdale | Green | FALSE | 4.00 | 1.00 | 4.00 |
| Bluffdale | Green | FALSE | 4.50 | 1.00 | 3.50 |
| Bluffdale | Green | FALSE | 5.00 | 1.00 | 2.50 |
| Provo_Mouth | Gray | TRUE | 6.50 | 2.00 | 4.00 |
| Provo_Mouth | Gray | TRUE | 6.00 | 1.00 | 4.00 |
| Provo_Mouth | Gray | TRUE | 5.50 | 1.00 | 2.00 |
| Provo_Mouth | Gray | TRUE | 5.50 | 1.00 | 3.00 |
| Provo_Mouth | Gray | TRUE | 5.50 | 1.00 | 2.00 |
| Provo_Mouth | Gray | TRUE | 7.00 | 1.50 | 2.50 |
| Provo_Mouth | Gray | TRUE | 7.50 | 1.50 | 3.50 |
| Provo_Mouth | Gray | TRUE | 5.50 | 1.00 | 3.00 |
| Provo_Mouth | Gray | TRUE | 7.00 | 1.50 | 3.50 |
| Provo_Mouth | Gray | TRUE | 6.00 | 1.50 | 3.00 |
| Provo_Mouth | Green | TRUE | 6.00 | 1.00 | 1.50 |
| Provo_Mouth | Green | TRUE | 5.50 | 1.00 | 2.50 |
| Provo_Mouth | Green | TRUE | 5.50 | 1.00 | 3.00 |
| Provo_Mouth | Green | TRUE | 4.50 | 0.80 | 2.25 |
| Provo_Mouth | Green | TRUE | 4.50 | 0.80 | 2.00 |
| Canyon_View | Gray | TRUE | 7.00 | 1.25 | 3.00 |
| Canyon_View | Gray | TRUE | 7.00 | 1.00 | 2.00 |
| Canyon_View | Gray | TRUE | 6.00 | 1.00 | 2.00 |
| Canyon_View | Gray | TRUE | 6.00 | 1.50 | 2.50 |
| Canyon_View | Gray | TRUE | 6.50 | 1.00 | 2.50 |
| Canyon_View | Gray | TRUE | 6.00 | 1.00 | 3.00 |
| Canyon_View | Gray | TRUE | 6.00 | 1.00 | 3.00 |
| Canyon_View | Gray | TRUE | 6.00 | 1.00 | 3.00 |
| Canyon_View | Gray | TRUE | 7.00 | 1.00 | 4.00 |
| Canyon_View | Gray | TRUE | 6.50 | 1.50 | 3.50 |
| Canyon_View | Green | TRUE | 6.00 | 1.00 | 1.50 |
| Canyon_View | Green | TRUE | 5.50 | 1.00 | 2.00 |
| Canyon_View | Green | TRUE | 4.80 | 1.50 | 2.15 |
One important difference in many plants is the success of their
seeds. Seed germination and days till germination can vary widely
between plant species. These factors may cause speciation within
clusters of sympatrically growing seed plants (Willis et al., 2014).
Some plants will put large energy resources into their seeds, allowing
for a greater percent germination of their seeds. On the other hand some
plants can create more seeds with lower germination and succeed in
spreading many propagules with a small but acceptable germination rate.
The timing of the germination event can also play a key role in
ecological separation as a delay of several weeks may cause plants with
differing germination to develop differently.
This data set
shows germination percentages for each site and how many days it took
each genotype to germinate.
| site | germ_per | day_till | color | lat | long | elevation_m | decid |
|---|---|---|---|---|---|---|---|
| Tabiona | 50 | 17.00 | Gray | 40.35184 | -110.7108 | 1985 | TRUE |
| Tabiona | 10 | 5.00 | Green | 40.35184 | -110.7108 | 1985 | FALSE |
| Tabiona | 30 | 9.00 | Gray | 40.35184 | -110.7108 | 1985 | TRUE |
| Tabiona | 50 | 11.80 | Green | 40.35184 | -110.7108 | 1985 | FALSE |
| Provo_Overlook | 30 | 50.00 | Gray | 40.32350 | -111.6326 | 1612 | FALSE |
| Canyon_View | 20 | 41.50 | Gray | 40.32505 | -111.6441 | 1491 | TRUE |
| Canyon_View | 30 | 9.00 | Gray | 40.32505 | -111.6441 | 1491 | TRUE |
| Canyon_View | 30 | 10.30 | Green | 40.32505 | -111.6441 | 1491 | TRUE |
| Canyon_View | 50 | 14.00 | Green | 40.32505 | -111.6441 | 1491 | TRUE |
| Lehi_Highway | 40 | 15.75 | Green | 40.44369 | -111.9065 | 1406 | TRUE |
| Lehi_Highway | 50 | 12.40 | Green | 40.44369 | -111.9065 | 1406 | TRUE |
| Lehi_Highway | 20 | 5.00 | Gray | 40.44369 | -111.9065 | 1406 | FALSE |
| Lehi_Highway | 40 | 13.00 | Gray | 40.44369 | -111.9065 | 1406 | FALSE |
| MTEC_Lehi | 70 | 7.57 | Green | 40.42186 | -111.8921 | 1383 | TRUE |
| MTEC_Lehi | 80 | 6.25 | Green | 40.42186 | -111.8921 | 1383 | TRUE |
| MTEC_Lehi | 10 | 53.00 | Gray | 40.42186 | -111.8921 | 1383 | TRUE |
| Inlet_Park | 20 | 5.00 | Gray | 40.35732 | -111.8982 | 1371 | FALSE |
| Inlet_Park | 30 | 4.00 | Gray | 40.35732 | -111.8982 | 1371 | FALSE |
| Inlet_Park | 80 | 17.80 | Green | 40.35732 | -111.8982 | 1371 | TRUE |
| Inlet_Park | 50 | 15.20 | Green | 40.35732 | -111.8982 | 1371 | TRUE |
| Bluffdale | 20 | 10.00 | Gray | 40.48013 | -111.9251 | 1363 | FALSE |
| Bluffdale | 50 | 25.00 | Green | 40.48013 | -111.9251 | 1363 | FALSE |
| Bluffdale | 30 | 19.00 | Green | 40.48013 | -111.9251 | 1363 | FALSE |
| Bluffdale | 40 | 12.00 | Gray | 40.48013 | -111.9251 | 1363 | FALSE |
| Midvale | 40 | 5.00 | Gray | 40.59948 | -111.9191 | 1306 | FALSE |
| Midvale | 50 | 8.00 | Gray | 40.59948 | -111.9191 | 1306 | FALSE |
| Midvale | 80 | 15.00 | Green | 40.59948 | -111.9191 | 1306 | FALSE |
| Midvale | 70 | 20.00 | Green | 40.59948 | -111.9191 | 1306 | FALSE |
| Provo_Mouth | 10 | 8.00 | Gray | 40.30984 | -111.6568 | 1465 | TRUE |
| Provo_Mouth | 20 | 15.00 | Gray | 40.30984 | -111.6568 | 1465 | TRUE |
| Provo_Mouth | 70 | 22.00 | Green | 40.30984 | -111.6568 | 1465 | TRUE |
| Provo_Mouth | 50 | 29.00 | Green | 40.30984 | -111.6568 | 1465 | TRUE |
Now to looking at how morphological traits and germination rates relate.
This box plot shows us that green genotypes have a higher
germination percent and shorter corolla length compared to the gray
genotype that has lower germination percent and longer corolla lengths.
Let’s do some statistical testing to see if any of these depictions are
significant!
## List of 10
## $ statistic : Named num -17.7
## ..- attr(*, "names")= chr "t"
## $ parameter : Named num 126
## ..- attr(*, "names")= chr "df"
## $ p.value : num 5.07e-36
## $ conf.int : num [1:2] -35.8 -28.6
## ..- attr(*, "conf.level")= num 0.95
## $ estimate : Named num [1:2] 5.38 37.62
## ..- attr(*, "names")= chr [1:2] "mean of x" "mean of y"
## $ null.value : Named num 0
## ..- attr(*, "names")= chr "difference in means"
## $ stderr : num 1.82
## $ alternative: chr "two.sided"
## $ method : chr "Welch Two Sample t-test"
## $ data.name : chr "Morph_Germ$corolla_length and Morph_Germ$germ_per"
## - attr(*, "class")= chr "htest"
Running a Ttest helps to see that since the p-value is < 0.5 that
the germination percent and corolla length depending on the genotype of
rabbitbrush is significant. There is quite a difference between the two
color groups.